Without making a concerted effort to do so, Cobain was being as inclusionary as he could within the confines of his genre. It's something you hear echoes of in Jack White's work and in his previous albums with the White Stripes and it's something the Black Keys have reached for in their own blues-based fuzz rock and their collaborations with artists from various genres. Inclusion is the common thread. It's what our Rocco Pendola hinted at when discussing how Pandora ( P) could further bridge the divide between artists and fans. It's what our Carlton Wilkinson is hinting at when he suggests that music is now less of a commodity and more of a collective social experience. More importantly, it was what Judd Apatow was getting at in his film This Is 40. At one point, the head of a nostalgia record label played by Paul Rudd hears his wife and kids listening to Nicki Minaj and counters by playing Alice In Chains' Rooster, a song about a marginalized, PTSD-addled Vietnam vet. His wife, Leslie Mann, responds by noting "You're the only one in this room that's happy," leaving Rudd to lament being the only male in the family. Music's role isn't limited to that of a mood enhancer. Morrissey wouldn't have a career and Bill Withers' Ain't No Sunshine wouldn't exist if that were the case. But neither the stadium-sized posturing of low-grade lechers dreaming of being the next Robert Plant nor the backwards-capped growling of Fred Dursts in training have broad-reaching appeal these days. Even would-be Mick Jaggers tend to sound more like Adam Levine of Maroon 5. That's ultimately the key lesson from Nirvana and Smells Like Teen Spirit: It changed music and, more specifically, rock music by making "rock" sound nothing like Nirvana. The music industry has long since rid itself of its sour post-grunge aftertaste and made a very poppy world amenable to rock again. According to Nielsen, rock was the leading genre last year, with 324 million tracks sold, more than the 303 million pop tracks sold during the same span. Adele's 21 may be the closest the digital music world got to a consensus in 2012, but the fact that roots-rock acts such as Mumford & Sons, the Lumineers and Of Monsters And Men accounted for four of the Top 10 downloaded albums last year is proof rock isn't out of the mix. It's just mellowed out a little bit and let more people into the show. -- Written by Jason Notte in Portland, Ore. >To contact the writer of this article, click here: Jason Notte. >To follow the writer on Twitter, go to http://twitter.com/notteham. >To submit a news tip, send an email to: email@example.com.